(1) Field of Invention
This invention relates to novel methods for preparing fluorinated organic compounds, and more particularly to methods of producing fluorinated olefins.
(2) Description of Related Art
Hydrofluorocarbons (HFC's), in particular hydrofluoroalkenes such tetrafluoropropenes (including 2,3,3,3-tetrafluoro-1-propene (HFO-1234yf) and 1,3,3,3-tetrafluoro-1-propene (HFO-1234ze)) (HFO is hydrofluorolefin) have been disclosed to be effective refrigerants, fire extinguishants, heat transfer media, propellants, foaming agents, blowing agents, gaseous dielectrics, sterilant carriers, polymerization media, particulate removal fluids, carrier fluids, buffing abrasive agents, displacement drying agents and power cycle working fluids. Unlike chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), both of which potentially damage the Earth's ozone layer, HFCs do not contain chlorine and thus pose no threat to the ozone layer.
Several methods of preparing hydrofluoroalkanes are known. For example, U.S. Pat. No. 4,900,874 (Ihara et al) describes a method of making fluorine containing olefins by contacting hydrogen gas with fluorinated alcohols. Although this appears to be a relatively high-yield process, for commercial scale production the handling of hydrogen gas at high temperature raises difficult safety related questions. Also, the cost of producing hydrogen gas, such as building an on-site hydrogen plant, can be in many situations prohibitive.
U.S. Pat. No. 2,931,840 (Marquis) describes a method of making fluorine containing olefins by pyrolysis of methyl chloride and tetrafluoroethylene or chlorodifluoromethane. This process is a relatively low yield process and a very large percentage of the organic starting material is converted in this process to unwanted and/or unimportant byproducts, including a sizeable amount of carbon black. The carbon black is not only unwanted, it tends to deactivate the catalyst used in the process.
The preparation of HFO-1234yf from trifluoroacetylacetone and sulfur tetrafluoride has been described. See Banks, et al., Journal of Fluorine Chemistry, Vol. 82, Iss. 2, p. 171-174 (1997). Also, U.S. Pat. No. 5,162,594 (Krespan) discloses a process wherein tetrafluoroethylene is reacted with another fluorinated ethylene in the liquid phase to produce a polyfluoroolefin product.
Catalyzed hydrogen reduction reactions have been disclosed for the preparation of fluorinated C3 hydrocarbons in U.S. Pat. No. 5,545,777. The patent describes the reaction as being one in which a compound of formula (1)C3HaClbFc  (1)is converted by catalyzed hydrogen reduction to a compound of formula (2)C3Ha+xClb−yFc−z  (2)where a, b, c, x, y and z are integers satisfying the following conditions: a≧0, b≧1, c≧2, x≧1, y≧1, z≧0, a+b+c=8, x=y+z, b−y≧0, and c−z≧2. Since the reactions disclosed in this patent require a reaction product in which a+b+c=8 and that x=y+z, it is not possible for the disclosed reaction product to include C3 olefins, which as mentioned above have been found to be desirable for use in many important applications.
Notwithstanding prior teachings applicants appreciate a continuing need for methods of efficiently preparing certain hydrofluorocarbons, particularly tetrafluorpropenes such as HFO-1234yf.